Our goal is to understand the process of visual transduction. Only when this mechanism is fully elucidated can one design meaningful approaches to visual disorders arising from the malfunction of this transduction process. Our hypothesis is that by using retinal analogues to specifically induce changes deep within the rhodopsin protein, it may be possible to modify the transduction mechanism. Our approach is to use analogues of the native chromophore, 11-cis retinal, to probe the site at which the visual process is initiated. The retinal analogues present the unique opportunity to gain information on changes within the rhodopsin protein itself without disrupting the native system. By using a variety of analogues to test specific chemical and electronic interactions of the chromophore with the protein, we propose to undertake the following series of experiments in collaboration with other laboratories: 1) Incorporation of analogues into the living isolated photoreceptors of vertebrate (tiger salamander) and an invertebrate (Limulus) for the purpose of studying effects on the discrete electrical events in transduction. 2) Correlation of G protein and phosphodiesterase activation with metarhodopsin states of the analogue pigments. 3) Determination of the exact location of the chromophore within the visual pigment in the rhodopsin and metatrhodopsin states by photoaffinity labeling followed by mass spectral analysis. 4) Studies of the structure-function role of retinal in a number of aspects of rhodopsin chemistry. 5) Determination in vitro of the properties of invertebrate analogue pigments. These studies will generate a better understanding of the transduction process which may have important implications in certain human disease processes.